The present invention relates to an improved photoelectric conversion device.
A typical device capable of converting light energy into electricity throughout a wide range of wave length is a solar cell incorporating amorphous semiconductor layer. An example of such a solar cell is illustrated in FIGS. 1(A) and 1(B). The solar cell is designed tandem and comprises three cell units 20, 20' and 20" arranged in series between a transparent substrate 11' and a back substrate 11'. The cell units 20, 20' and 20" are composed respectively of p-type semiconductors 13, 13' and 13", i-type semiconductors 14, 14' and 14" and n-type semiconductor 15, 15' and 15". Each layers are fabricated by glow discharge plasma CVD on the substrate 11' and the transparent substrate 11 is covered thereon through a transparent resin layer 5.
Whereas such a solar cell of this prior art is suitable in mass production since each layer can be formed on the preceding one in sequence, a defect(pinhole) on one cell unit reduces the whole cell to impotence and the yield of the production of this cell is remarkably decreased.
Further, in the tandem cell the cell units 20, 20' and 20" have to be arranged so that the closer a cell unit is located to the incident side, the wider the energy gap of a cell unit is and the thinner the intrinsic semiconductor layer of the cell unit is, in order to carry out conversion of light having short wave length without undesirable thermally absorption of light in a preceding cell unit. The intrinsic semiconductor layer 14, 14' and 14" are made of SixGe.sub.1-x (0&lt;x&lt;1). To comply with the above requirement on band gap, x is chosen 1 for the layer 14, 0.8 for the layer 14' and 0.6 for the layer 14". Namely the Ge density of a thicker layer must be higher than a thinner layer. It reduces the economical advantage of an amorphous silicon semiconductor solar cell.